Congress has to pass a proposal to fund the government and the president needs to sign it before another partial government shutdown this Friday.
Republicans tentatively agreed to far less money for Trump's border wall than the White House's $5.7 billion wish list, settling for a figure of almost $1.4 billion, according to congressional aides.
"We stand for America and we stand against walls", O'Rourke told the cheering crowd. Local officials also have said that the physical barrier has had no effect on the city's relatively low rate of violent crime.
Trump has repeatedly pointed to El Paso to make his case that a border wall is necessary, claiming that barriers turned the city from one of the nation's most unsafe to one of its safest.
But according to an analysis of Federal Bureau of Investigation crimes data and city law enforcement data analyzed by the El Paso Times, violent crime in the city peaked in 1993. "So we have, let's say, 35,000 people tonight, he has 200 people, 300 people - not too good", Trump claimed.
He says, "Walls do not save lives, walls end lives", citing the danger to asylum seekers who are rejected by the U.S. Fellow Republicans have told Trump such a step would nearly certainly face a legal challenge.
Trump has insisted that large portions of the wall are already underway.
The whole rally largely stuck to Trump's usual talking points - ticking off economic successes, trade deals, boasting about his relationship with North Korean leader Kim Jong Un and rehashing much of what he had said last week in his State of the Union address.
As Trump traveled to the site of his Monday rally, negotiators on Capitol Hill announced that lawmakers had reached an agreement in principle to fund the government ahead of a midnight Friday deadline to avoid another shutdown.
"That may be the end of his presidential bid", Trump quipped, adding: "You're supposed to win in order to run".
Estimates of how many people were at O'Rourke's protest aren't exact, but the number appears to be at least 5,000, according to several reports. Jennifer Epstein of Bloomberg News reported that march and rally drew between 10,000 and 15,000 people.
Fire Department spokesman Enrique Aguilar told the El Paso Times that no such permission was given and the coliseum only had the 6,500 capacity that it holds.
"Here in one of the safest cities in the United States of America".
He also criticized the Trump administration's treatment of immigrants, from separating children from adults at the border to housing migrants in detention centers, and just a general vilification of the contributions of immigrants. "We are going to show the country who we are. That is the way we make our communities and our country safe". But O'Rourke said only, "This is where we make our stand".
"The Democrats do not want us to detain, or send back, criminal aliens!" He tells them "to keep up that fight, bring it to your schools".
He repeated his warnings about drugs and human traffickers coming over the border, and argued Democratic attempts to bolster security at ports of entry won't help. "The Democrat Party has never been more outside of the mainstream", he said. Somewhere in his rambling remarks Monday night, Trump said, "The biggest proponents of open borders are rich liberals and wealthy donors", and called them hypocrites who oppose security for ordinary Americans while living their entire lives protected and secure.
"If we cut detention space, we are cutting loose risky criminals into our country", he said.